Former Red Devil's skipper Wayne Rooney advises new signing Lukaku that he has to maintain his performance at Manchester United.

Former Manchester United star Wayne Rooney on Sunday asked the club's newly signed striker Romelu Lukaku to stay mentally strong for the challenges ahead. The 24-year-old Belgian striker Lukaku last week joined record English football champions Manchester United from Everton on a five-year contract with a reported transfer fee of 75 million pounds ($98.19 million).

"You've got to be strong enough mentally to accept the challenge, United are a football club that demands success. Romelu has to be strong enough to take up that challenge," says Rooney.

The 31-year-old Rooney, who left the Manchester club to join his boyhood club Everton after holding the record of being their highest goal scorer with 253 goals, also said playing for his previous side will put some characters into test.

"Playing for Manchester United is a test of character," Rooney said.

"Hopefully, Romelu has got people there who will give him the right guidance and get the best out of him," he added.

The Everton striker also said playing for his former side will need Lukaku to match his standards with the club's former star players.

"There are standards that you have to keep when you are at Manchester United. That came from (former head coach) Alex (Ferguson) when I went to United and it was passed down through the likes of Giggsy (Ryan Giggs), Gary Neville and Scholesy (Paul Scholes)."

"Over the last few years, it was down to me and Michael Carrick to keep the new players maintaining those standards."

"That has been more difficult over the last few years, with some of the players who joined the club. There are traditions at United that have to be maintained," Rooney said.